The invention relates generally to chain saws and, more particularly, to arrangements for guiding a saw chain between the sprocket and the cutter bar.
More particularly, there is shown in FIGS. 1 through 3, a prior chain saw 13 which includes a supporting frame 15, an engine 17 supported by the frame 15, and a drive shaft 19 rotatably carried by the frame 15 and driven by the engine 17. The drive shaft 19 carries a centrifugal clutch 21 which, in response to drive shaft rotation, drivingly couples the drive shaft 19 to a chain sprocket 23 rotatably supported by the drive shaft 19.
Also supported by the frame 15 is a cutter bar 25 having (See FIG. 3) a peripheral groove 27 bordered by a pair of spaced margins 29. Trained around the sprocket 23 and extending in the cutter bar groove 27 is a saw chain 31 which typically includes in series, a pair of side links 33 pivotally connected to one end of a center link 35 located therebetween by a rivet 37. In turn, the other end of the center link 35 extends between another pair of side links 33 and is pivotally connected thereto by another rivet 37. The last mentioned pair of side links 33, are, in turn, pivotally connected by another rivet 37 to another center link 35 which, in turn, is pivotally connected by another rivet 37 to still another pair of side links 33 and so on. The center links 35 include depending drive tangs 39 which are engaged by the sprocket 23 to drive the chain 31 and which extend into the cutter bar groove 27 to guide the chain 31 during travel around the periphery of the cutter bar 25. The side links 33 ride on the margins 29 of the cutter bar groove 27 and every other pair of side links 33 includes a cutting tooth 41.
The cutter bar 25 is clamped to the frame 15 by means including two mounting posts 35 which extend fixedly from a frame portion 47 laterally adjacent to one end 49 of the cutter bar 25, which extend through a lengthwise slot 51 in the cutter bar end 49 so as to permit lengthwise movement of the cutter bar 25 relative to the chain sprocket 23 so as thereby to adjust chain tension, and which extend through apertures in a sprocket or chain guard or member 55. In this regard, the sprocket guard 55 extends generally in covering relation to the chain sprocket 23 and centrifugal clutch 21 and includes a clamping portion 57 which includes the apertures and which extends in laterally adjacent relation to the cutter bar end 49. Application of nuts 59 to the posts 35 serves to clamp the sprocket or chain guard 35 to the supporting frame 15 with the cutter bar 25 therebetween.
When assembled to the frame 15, the cutter bar end 49 is spaced somewhat from the sprocket 23 and includes a concavely arcuate edge 61 from which upper and lower end margin portions 63 and 65 respectively, extend in diverging relation in the direction away from the edge 61. The chain 31 extends generally tangentially (with some sag) from the top and bottom of the sprocket 23 to points of engagement of the side links 33 with the margins 29 of the cutter bar 25. The end portions 63 and 65 of the cutter bar margins converge in the direction toward the sprocket 23 from such points of chain engagement at a rate greater than the chain 31. Thus, the center link drive tangs 39 gradually enter and leave the peripheral cutter bar groove 27 and the side links 33 gradually approach and depart from the cutter bar margins 29.
In order to assist entry of the chain 31 onto the cutter bar 25 from the sprocket 23 and departure of the chain 31 from the cutter bar 25 and entry onto the sprocket 23, inner and outer guide plates 71 and 73 respectively are fixedly located between the cutter bar 25 and each of the frame portion 47 and the clamping portion 57 of the sprocket guard 55. Specifically, the inner guide plate 71 is located between the cutter bar 25 and the frame portion 47 and the outer guide plate 73 is located between the cutter bar 25 and the clamping portion 57 of the sprocket guard 55. In the past, as shown best in FIG. 2, each of the guide plates 71 and 73 included a central, generally flat, main part 75 having upper and lower edges 77 and 79, respectively, which diverged outwardly in the direction away from the chain sprocket 23. More specifically, the upper and lower edges 77 and 79 each included a portion 81 adjacent to the converging guide plate end and a portion 83 which diverges less rapidly as compared to the portion 81 and which is located at the divergent guide plate end.
In addition, each of the guide plates 71 and 73 included, along the upper and lower edges 77 and 79 of the main part 75 thereof, respective upper and lower outwardly divergent wing portions 85 and 87 which, together, formed fixedly located, upper and lower V-shaped guide ways 91 and 93 extending along the upper and lower edges 77 and 79 of the main part 75 in adjacently spaced relation from the sprocket 23 to the cutter bar margins 29, notwithstanding adjustment of the cutter bar 25 relative to the sprocket 23 as mentioned above.